Method and device for adjusting the colour density on material to be printed

ABSTRACT

The invention relates to a rotary printing press comprising at least one inking roller ( 3, 4 ), which transports printing ink, composed essentially of pigments and solvent, from an ink reservoir ( 2, 12 ) towards the material to be printed ( 5 ). The intensity of colour on the material to be printed ( 5 ) is adjusted by means of the mixing ratio of pigments to solvent in the colour that is transferred to the material to be printed ( 5 ). The mixing ratio of pigments to solvent in the ink can be influenced by a device that aids the evaporation of the solvent, said device acting on one of the inking rollers ( 3, 4 ).

The invention has to do with a mechanism for setting the density of inkdots on a print substrate according to the first portion of Claim 1.

Rotary printing machines possess at least one ink transfer roller whichconveys towards a print substrate ink from an ink reservoir, which as arule is an ink pan or a coater chamber supplied with ink from an inktank. With flexoprinting machines of the more recent type ofconstruction both the anilox roller, which conveys ink from the inkchamber coater to the press plate, as well as the press plate itselfthat takes up ink from the anilox roller and further conveys it to theprint substrate, are ink transfer rollers as defined in the invention athand. With rotogravure only the gravure cylinder is to be characterizedas an ink transfer roller.

The formulation “towards” in the first portion of Claim 1 is to beunderstood in reference to the transfer direction of the ink by means ofthe respective rollers.

With the printing process on rotary printing machines it is oftendesired to alter the intensity of the hue to be applied to the printsubstrate. The intensity effect is caused by means of the density of theink.

Various options exist to influence the intensity of a hue on the printsubstrate. The ink density on the print substrate on the one hand isinfluenced by the quantity of printing ink applied. The quantity of theink applied is thereby often influenced in that the color separation isvaried between the individual rollers involved in the printing process.For this purpose the viscosity of the printing ink is influenced. Withthe varying quantity of ink transferred by means of the rollers,however, the layer densities applied to the print substrate can bedifferent.

As an alternative thereto the ink density on the print substrate canalso be set by means of the ratio of color pigments to solution in theprinting ink. With such a familiar type of method the ink density firstis measured with an appropriate measuring device, somewhat like adensitomer, in order to set the ink density on the print substrate. Inorder now to be able to vary the ink density, the ratio of ink particlesto solutions in the ink supply tank must be modified. The ratio of inkparticles to solutions in the ink supply tank is modified by refillingconcentrated printing ink and/or solution. This is very laboriousbecause this process often becomes necessary several times, often leadsto inconclusive results and all the old ink must be uniformly thoroughlymixed in with the ink components added later in order to obtain a stableprint image. For this reason the printing process often even has to beinterrupted.

For this reason the task for the invention at hand consists in proposinga method and a mechanism that provide the option of being able toinfluence the ink density on the print substrate without refillingprinting ink and/or solution into the ink tank.

The problem is resolved by means of the distinguishing characteristicsof Claim 1.

Preferably bellows are planned for supporting the evaporation of thesolution. They blow a suitable gas, for example air, onto one of the inktransfer rollers so there is an exchange of ambient air enriched withsolutions.

Particularly advantageous is the arrangement of suckers for supportingevaporation of the solution. With aid of such a sucker the volume streamof an appropriate gas, for example air, led by the ink transfer rolleris increased so that even here there is an exchange of enriched ambientair with solutions.

Of course besides the bellows other functional units supportingevaporation can be assigned to the ink transfer roller as well. Thesecan be infrared, microwave or other radiation emitting devices thatirradiate the ink on the ink transfer roller. Moreover, mechanisms forseparating laminar border layers adhering to moved parts can beutilized. It is known that these laminar border layers have a starkadverse effect on air exchange and thereby evaporation. The separatingof a laminar border layer is necessitated by means of mechanicalcomponents, for example the turbulence generators depicted in DE 100 34708 A1, but also by means of electrical and/or magnetic fields (cf. DE195 25 453 A1 and DE 100 50 301 A1). Finally, mechanisms for heating upof the ink transfer rollers can also be designed.

It is particularly advantageous to arrange between the blower and thenext ink transfer roller a second ink reservoir, which provides theoption of applying additional ink to the ink transfer roller. Thus thevolume loss arising by means of evaporation of solution can be offset sothat even with various evaporation rates of the solution the samevolumes of printing ink are still transferred to the next ink transferrollers.

In order to have a most varied possible ability to influence the inktransfer roller, in an additional preferred embodiment at least oneadditional mechanism for supporting evaporation is planned that has aneffect on another part of the scope of an ink transfer roller.

In a particularly preferred arrangement, in the direction of inktransfer in the printing machine a mechanism for supporting evaporationof solution on an ink transfer roller in each case follows each inkreservoir through which the ink is applicable to an ink transfer roller.

In order to be able purposefully to influence the quantity of colorpigments that are finally applied to the printing substrate, the outputof the mechanisms for supporting evaporation of the solutions iscontrollable and/or adjustable.

A rotary printing machine according to the invention:

With the invention-related method for setting the ink intensity on aprint substrate, the mixing ratio of color pigments and solution in theprinting ink is set by purposefully influencing the evaporation ofsolutions on one of the ink transfer rollers. In this way the density ofthe ink on the print substrate can be controlled without having tointerrupt the printing process.

The individual figures show:

FIG. 1 A sketch of the familiar method and of the related mechanism forapplying printing ink to the print substrate

FIG. 2 A sketch of the invention-related method and the relatedMechanism for lowering the ink density

FIG. 3 Sketch of a mechanism for implementing the method for raising theink density

FIG. 4 Sketch of a mechanism for implementing the method for raising orlowering ink density

FIG. 1 shows a sketch of the implementation of the generally commonmethod for application of printing ink to a print substrate with the aidof a familiar rotary printing machine=s inking unit 1. The printing inkis introduced from an ink tank not depicted via lines and pumps also notshown through ink chamber coating 2 in a way that the ink chambercoating 2 always contains a certain volume of printing ink. The inkchamber coating 2 is thereby to be regarded as an ink reservoir. Now ifthe ink chamber coating 2 traverses an ink fountain 8 of the aniloxroller 3 then this fountain 8 is subsequently filled to the brim withprinting ink and thus reaches the printing roller 4. The printing roller4 now takes up a part of the printing ink. A certain remainder of theprinting ink remains, though, in the fountain 8. This type of breakingup of the printing ink is generally characterized as color separation.Upon another traversing of the ink stored in the ink chamber coater 2the reservoir is again filled up to the upper brim so that the inktransfer process can start once more.

The printing roller 4 conveys printing ink onto the print substrate 5 inan inherently familiar way, whereby the print substrate 5 that isintroduced by a guide roller 7 rests on a counter-pressure cylinder 6.

The FIG. 2 shows a mechanism that serves to lower the ink density on theprint substrate 5 when necessary. An air hose 9 is attached to theanilox roller 3 in this case in the transfer direction behind the inkchamber coater 2. Now if the ink chamber coater 2 traverses theconsidered fountain 8, then the latter is completely filled withprinting ink. Subsequently, the filled fountain 8 is blown onto with theaid of the Controllable air nozzle 9. Thus the evaporation of solutioncontained in the printing ink is increased leading to more colorpigments being transferred on the print substrate during an inkapplication of equal volume. This condition, as already mentioned manytimes, would lead to a more intensive color impression on the printsubstrate. With the embodiment pursuant to FIG. 2, however, the printingink fill level has been lower in the ink fountain 8.

The delivery of ink to the printing roller 4 is made difficult by thiscondition, since a poorer contact occurs between printing ink andprinting roller 4 if the ink fountain 8 in the coater roller 3 is notfilled to its upper rim. The color separation is thus modified. For thisreason, with the embodiment pursuant to FIG. 2, less ink is transferredthan with the mechanism shown in FIG. 1, where the mixing ration is notinfluenced in the invention-related way. At any rate, with thisembodiment it can also come down to a rise in the ink intensitydepending on the type and transfer ratio of the printing ink. This isparticularly the case if with a relatively slight rise in the inkevaporation on the rollers 3, 4 involved in ink transfer, the inkfountains 8 are still filled to the extent that the ink transfer ishardly adversely affected while the concentration of the color pigmentsin the ink already increases noticeably. In both cases, however,noticeable modifications in the print image can be brought about withoutthe ink composition in the ink tank having to be changed.

FIG. 3 shows a mechanism that can be used in any operating condition fora distinct heightening in the intensity of the color on the printsubstrate 5. Increasing a portion of the color pigments in the printingink achieves this result. Here two ink chamber coaters 2, 12 are plannedthat are arranged on the anilox roller 3. An air nozzle 9 is arrangedbetween these two ink chamber coaters 2, 12. The considered fountain 8first traverses the ink chamber coater 2 and is completely filled withprinting ink. Subsequently blown air from the air nozzle 9 arrives onthe ink fountain 8 so that even here again solution is quicklyevaporated and in the remaining printing ink the portion of colorpigments is increased. Simultaneously a film builds up on the surface ofthe remaining printing ink. When traversing the second ink chambercoater 12 the ink fountain 8 is filled again to the upper rim. At thesame time the film prevents the printing ink already located in the inkreservoir 8 from being exchanged. The increased portion of colorpigments thus remains intact, even after adding fresh printing ink.

On the way between the second ink chamber coater 12 and the printsubstrate 5 fresh ink is now able to etch the film. Both parts of theprinting ink can commix. The printing ink now contained in the inkfountain 8 has a slightly elevated color pigment portion in relation tothe original printing ink. On the print substrate 5, an increased inkdensity can be subsequently observed that leads to a heightenedintensity in the corresponding color.

With the mechanism shown in FIG. 4, the color pigment portion in theprinting ink can be raised or lowered as need be. For this reason, themechanism shown in FIG. 3 has been expanded by an additionalcontrollable air nozzle 19 that is arranged in the transfer directionbehind the second ink chamber coater 12. First, the considered inkfountain 8 in the ink chamber coater 2 completely filled with printingink. After traversing the bellows stream from the air nozzle 9, lesssolution is located in the printing ink and a film has built up. Whiletraversing the second ink chamber coater 12 the missing ink in the inkreservoir 8 is introduced. The second air nozzle 9 is arranged in such away that it then blows onto the ink fountain 8 if the printing ink inthe ink reservoir has sufficiently commixed. The use of the second airnozzle 19 leads to the additional evaporation of solution so that on theone hand the fill volume of the ink reservoir 8 is decreased butsimultaneously the ink particle portion is raised. Using the appropriatesettings on both the air nozzles 9, 19, this method allows for the inkdensity on the print substrate 5 to be finely adjusted with regard tothe ink density preset by the printing ink and other parameters ofinfluence so that various color intensities are represented without theprinting process having to be interrupted. List of Reference Codes 1Inking unit 2 Ink chamber coaler 3 Ink transfer roller 4 Printing roller5 Print substrate 6 Counter-pressure cylinder 7 Guide roller 8 Inkfountain 9 Air nozzle 10 11 12 Ink chamber coater 13 14 15 16 17 18 19Air nozzle 20 21 22 23 24 25 26 27 28

1. Rotary printing machine with at least one ink transfer roller (3, 4),which transfers ink that particularly consists of color pigments andsolutions towards a print substrate (5) ink from an ink reservoir (2),whereby the intensity of the ink on the print substrate (5) isadjustable through the mixture ratio of the color pigments and thesolution in the ink that is transferred from the machine to the printsubstrate (5) characterized in that the mixture ratio of the colorpigments and the solution in the ink, which is transferred by themachine onto the print substrate (5) by means of at least one mechanismfor supporting evaporation of solution (9, 19) on at least one inktransfer roller (3, 4), is influenceable.
 2. Rotary printing machineaccording to claim 1, characterized in that it includes at least onemechanism for supporting evaporation of solution (9, 19) on the inktransfer roller (3, 4) that has a blower which blows a suitable gas suchas air onto the ink transfer roller (3, 4).
 3. Rotary printing machineaccording to claim 1 Characterized in that it includes at least the onemechanism for supporting evaporation of solution (9, 19) on the inktransfer roller (3, 4) and has a sucker which increases the volume flowof a suitable gas, such as air, that is led by the ink transfer roller.4. Rotary printing machine according to claim 1 Characterized in that itincludes at least one mechanism for supporting the evaporation ofsolution (9, 19) on the ink transfer roller (3, 4) with the followingfunctional units: radiant sources, as in particular infrared radiatorsor microwave emitting devices which spray the ink on at least one inktransfer roller, mechanisms for separating of the laminar border layeradhering to the ink transfer roller, mechanisms for heating up of atleast one of the ink transfer roller.
 5. Rotary printing machineaccording to claim 1 Characterized in that at least a second inkreservoir (12), which is arranged in the transfer direction between theink transfer roller (3, 4) and the mechanism for supporting evaporationof solutions (9, 19) on an ink transfer roller (3, 4) and through whichadditional ink can be applied to the in transfer roller (3, 4)
 6. Rotaryprinting machine according to claim 1 Characterized in that at least oneother mechanism for supporting of evaporation of solution (9, 19) has aneffect on at least one ink transfer roller (3, 4), which influencesanother part of the scope of the ink transfer roller (3, 4).
 7. Rotaryprinting machine according to claim 4 Characterized in that in each casein the ink transfer direction in the printing machine one mechanism forsupporting evaporation of solutions (9, 19) on at least one ink transferroller (3, 4) follows ink that is applicable onto an ink reservoir (2,12) through which ink can be applied onto an ink transfer roller (3, 4),8. Rotary printing machine according to claim 1 Characterized in thatthe output of mechanisms for supporting the evaporation of solution (9,19) on at least one ink transfer roller (3, 4) in operating the printingmachine can be controlled and/or regulated.
 9. Method for setting theink intensity on a print substrate (5) printed by a rotary printingmachine whereby the rotary printing machine is equipped with at leastone ink transfer roller (3, 4), which transfers ink toward a printsubstrate, that in particular consists of color pigments and solutions,from a ink reservoir (2, 12) in the direction of a print substrate (5),and whereby the intensity of the ink on the print substrate (5) is setthrough the mixing ratio of the color pigments and the solution in theink which is transferred by the machine characterized in that the mixingratio of the color pigment and the solutionis set by the evaporation ofsolution being supported on at least one ink transfer roller (3, 4).